Evidence of tunable magnetic coupling in hydrogenated graphene

Abstract

A lot of efforts have been devoted to understanding the origin and effects of magnetic moments induced in graphene with carbon atom vacancy, or light adatoms like hydrogen or fluorine. At the meantime, the large negative magnetoresistance (MR) widely observed in these systems is not well understood, nor had it been associated with the presence of magnetic moments. In this paper, we study the systematic evolution of the large negative MR of in-situ hydrogenated graphene in ultra-high vacuum (UHV) environment. We find for most combination of electron density (ne) and hydrogen density (nH), MR at different temperature can be scaled to 𝛼𝛼 = 𝜇𝜇 𝐵𝐵 𝐵𝐵 𝑘𝑘 𝐵𝐵 (𝑇𝑇 − 𝑇𝑇 * ) ⁄ , where T * is the Curie-Weiss temperature. The sign of T * indicates the existence of tunable ferromagnetic-like (T * >0) and anti-ferromagnetic-like (T * <0) coupling in hydrogenated graphene. However, the lack of hysteresis of MR or anomalous Hall effect below |T * | points to the fact that long-range magnetic order did not emerge, which we attribute to the competition of different magnetic orders and disordered arrangement of magnetic moments on graphene. We also find that localized impurity states introduced by H adatoms could modify the capacitance of hydrogenated graphene. This work provides a new way to extract information from large negative MR behavior and can be a key to help understanding interactions of magnetic moments in graphene.

In Situ Tuning of Magnetism in Fe3GeTe2 via Argon Ions Irradiation

“…In situ modification measurements can ensure that the physical properties are only affected by the intended modifications and exclude unwanted influences, thereby improving the accuracy of tuning particularly sensitive materials. In situ transport measurements have demonstrated unique advantages in materials such as Co-decorated graphene [29], hydrogenated graphene [30] and so on [31,32]. Therefore, combining tunable thin flake Fe 3 GeTe 2 with in situ transport provides an exciting opportunity to explore the mechanism of anomalous Hall effect and the tuning of magnetic properties.…”